Regeneration of central nervous pathways in the pulmonate snail Melampus bidentatus is being studied with behavioral, anatomical, and electrophysiological techniques. Transection of the cerebral commissure is followed by regrowth of the commissure in a few weeks and behaviors which depend upon cross-commissure communication gradually reappear during that time. Control of contraction of the labial area of the snail's face will be studied at the level of identified motoneurons and their normal synaptic inputs. The activity of these motor units will then be sampled in snails at various stages of regeneration and the extent of restoration of normal synaptic contacts and the degree of plasticity in the nervous system's response to injury will be evaluated. The role of the labial motoneurons during locomotion and the alteration of this behavior by various central nervous system lesions will be studied. Cobalt chloride backfilling and injection will be used to locate and mark neurons in the labial nerve reflex pathways. Electron microscopy will be used to study the fine structure correlates of regeneration.